The present invention is directed generally to staged, sequentially separated injection molds and particularly to molds for forming container spouts having an integral panel sealing the spout and an integral pull ring to facilitate opening the spout by removal of the panel.
Certain types of containers, such as cartons and the like that have a gable-shaped top, employ separately molded plastic spouts with threaded closures. Such cartons will be recognized as those containers in which quarts, liters, and half-gallons of milk or juice are packaged. The spouts are injection molded to include a removable integral panel sealing the spout at the time of initial purchase by the consumer. Examples of such an injection molded spout are found in U.S. Pat. Nos. 5,133,486; 5,735,426; 5,915,574; 5,957,312 and 6,179,147. The integral panel is view as a tamper-resistant feature of the closure system that is desired by the public to ensure the safety of the product within the container. The integral panel is joined to the spout by a frangible line, and an integral pull ring is provided to facilitate opening of the spout through removal of the integral panel by tearing the frangible line surrounding the panel. The spout includes a threaded exterior surface and a threaded closure to permit re-closing of the container after partial consumption of the contents.
To mold such spouts in an injection molding apparatus, a steel or other metallic mold of the item to be molded is first made. The mold contains a mold cavity configured to reflect the part to be molded. The mold is periodically openable, or separable, so that the molded part can be removed from the mold cavity. A plastic material, such as polypropylene, polystyrene or the like, is injected, such as by a reciprocating screw arrangement, into the mold. After the material has been allowed to cool, the mold is opened and the molded part is ejected from the mold. The mold can then be closed and used for forming a subsequent part.
The presence of the integral panel and pull ring on the interior of the spout at the time it is initially molded represents a special problem. The ejection of the part from the mold must occur in such a sequence as to preserve the frangible line surrounding the removable panel and the pull ring. This can be accomplished by having the mold include an internal mandrel-like core element or sleeve around which the plastic material is molded to conform to the desired mold shape. The mandrel-like portion must, as part of the mold opening sequence, be removed from the molded part after the part is formed. In some known injection mold apparatus, removing the mandrel-like mold element is typically done by pulling or stripping the molded part from the mandrel as part of the mold opening sequence. This, however, may cause damage to the molded parts, particularly if the parts include threads or pull rings formed therein.
One mold designed for this purpose, disclosed in U.S. Pat. Nos. 5,736,172 and 5,820,807, includes a plurality of concentric, separable telescopic mold elements, and an opening therein defined by one of the base portion and the mold elements for injecting a mold material into the apparatus. The elements are configured such that they can be separated or removed from the mold, from the inner most element outward. This structure is intended to provide sufficient free space for the newly molded part to flex inward as the mold elements are removed thus minimizing the possibility of damage to the molded part. Each of the mold elements includes a mold face, which in part defines a mold cavity, and flange portions opposite of their respective mold faces. The mold also includes a movable, ball bearing type to facilitate opening the mold for removal of the molded container spout. The mold apparatus also includes two intermediate mold elements positioned between the inner and outer mold elements. Each of the intermediate mold elements includes openings through their respective body portions adapted to receive a movable, locking ball bearing cam member therein.
This combination of separable telescopic mold elements and locking ball bearing cam members is rather complex and less reliable than would be desirable in a manufacturing situation. Thus, there continues to be a need for an injection molding apparatus which permits a staged, sequential separation of the mold to effect withdrawal of mold portions, which separation process eliminates the potential damage to the molded parts during the mold opening process.